An operation of GPS navigation systems is to acquire and track GPS satellite signals so that range measurements can be made between several satellites and a receiver in order to compute a location for the receiver. A metric of acquisition performance is time to first fix (TTFF). The TTFF can be dependent on the accuracy of the receiver's a priori estimate of GPS time within its local timing system.
While the receiver is off, the estimate of GPS time is typically maintained with a low power real time clock (RTC) based on a watch-class crystal oscillator. While such oscillators are low power, typically μW level, they are not very accurate. Specifically, the RTC typically suffers temperature dependent errors on the order of 200 PPM over typically specified operating temperature ranges, such as −40° C. to +85° C. Consequently, when the receiver is turned off and the RTC is maintaining time, the accuracy of the RTC time relative to GPS system time rapidly degrades.